Typically, normal reinforcing steel bars have good corrosion resistance in concretes. This is because the reinforcing steel bar will form a compact passivation film in a highly basic environment, and this layer of compact passivation film will prevent the evolution and development of corrosion. However, once the concentration of chloride ions in concrete exceeds a certain critical value, this layer of passivation film will have a drastically reduced stability or even will be broken down, finally resulting in remarkable corrosion of reinforcing steel bars. The expansion effect of corrosion products will accelerate the ineffectiveness of reinforced concrete structures.
As marine resources are developed by human beings, reinforced concrete facilities serving in the marine environment are in an environment with a high concentration of chloride ions, the resultant problems with the drastic reduction of the structural durability induced by the rust corrosion of reinforcing steel bars are increasingly severe. The same challenges are encountered in the cold areas where chloride salt snow melters are used in large quantities.
At present, the prevention techniques in the world for improving the corrosion resistance to chloride ions mainly comprises two following major types:
(1) Surface Coating Reinforcing Steel Bars.
A surface coating reinforcing steel bar blocks the channel between a corrosive medium and a reinforcing steel bar matrix by physical means so as to achieve the object of improving the corrosion resistance, and the main types are epoxy-coated reinforcing steel bars and hot-dip galvanized reinforcing steel bars. Although surface coating reinforcing steel bars have some application cases, there are still a plurality of drawbacks that cannot be overcome due to the limits of the processes themselves. For example, the breakage phenomena of coatings caused in the process of construction cannot be completely prevented, the epoxy-coated reinforcing steel bars will reduce the bond stress between concretes and reinforcing steel bars, and hot-dip galvanized reinforcing steel bars will damage concretes due to the volume expansion of the corrosion products of zinc, or the like.
(2) Matrix Corrosion-resistant Reinforcing Steel Bar
A matrix corrosion-resistant reinforcing steel bar refers to a reinforcing steel bar obtained by adding a corrosion-resistant alloy element to a normal reinforcing steel bar so as to improve the corrosion resistance of a reinforcing steel bar matrix. Intrinsically existing problems of surface coating reinforcing steel bars will not occur in matrix corrosion-resistant reinforcing steel bars, and the matrix corrosion-resistant reinforcing steel bar mainly include low-alloy corrosion-resistant reinforcing steel bars and stainless corrosion-resistant reinforcing steel bars.
The low-alloy corrosion-resistant reinforcing steel bar is one of research hotspots in recent years, and researchers have tried to add a small amount of corrosion-resistant alloy elements such as Ni, Cr, etc. to a normal reinforcing steel bar so as to improve the overall corrosion resistance of the reinforcing steel bar. Although the alloyed corrosion-resistant reinforcing steel bars have certain advantages compared to the surface coating reinforcing steel bars, very few successful applications have been reported so far. This is because the addition of a small amount of corrosion-resistant alloy elements is limited with respect to the improvement of the corrosion resistance of reinforcing steel bars, and it is still very difficult to meet the requirements for long-term safe services of reinforced concretes in high-chlorine environments. Stainless corrosion-resistant reinforcing steel bars, particularly two-phase stainless reinforcing steel bars, have excellent corrosion-resistant properties to high-chlorine environment corrosion, and the expected lifetime for safe service in most marine environments in the world exceeds one hundred years. However, their high production costs limit the large-scale applications thereof.
Therefore, the invention of a reinforcing steel bar product, which has a corrosion resistance to chloride ions reaching or even exceeding those of the existing stainless reinforcing steel bars and has a relatively low production cost, has an extremely large prospect for application. This invention forms a stainless surface layer, of which the chemical components meet the requirements for stainless and the corrosion resistance is excellent, on the surface of a reinforcing steel bar, by implementing a heat diffusion technique on a pre-formed reinforcing steel bar blank.